Martin Kettle's advice for Clegg:

Choose the right moment to remind the viewers that the Liberal Democrats were the only party that spoke for the British people over the Iraq war, that Brown still defends it and that Cameron voted for it. Make it an emblem of having good judgment, standing up for what is right, and speaking for the people not the old consensus.

John Kampfner makes the same point. But the war in Afghanistan may play a larger role today. Daniel Korski wonders how Europe will factor into the debate and into a possible Tory-Lib Dem government. I'll be live-blogging at 3.30 pm. It will be a critical moment in this election - and a debate that most directly affects the US.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.